Astronomy & Astrophysics

Astronomy & Astrophysics

  • Eric J. Hallman added an answer:
    What is the physical meaning of Integrated Sachs-Wolfe effect, and how is it different to the Rees-Sciama effect?

    I found some papers discussing ISW as a proof of dark energy, but what is its physical meaning? What is your opinion? And how to calculate it?

    Eric J. Hallman

    I think I didn't answer your question regarding the "physical meaning" of these effects.  Physically, they are a result of the frequency shifting of CMB photons due to the change in size of the gravitational potential they are traveling through during that travel time.  Meaning, the photon enters the potential, and is blueshifted traveling down into the potential well.  The large size of the cosmological potential wells means that as the photon travels, and is still under the influence of the object's gravity, it can grow in mass, deepening the potential.  Therefore, when the photon climbs out of the potential, being redshifted by that travel, the corresponding redshift from leaving the deeper potential is larger than the size of the blueshift it encountered when entering the potential.  Therefore, on scales relevant to the size of the potentials that are important (for ISW it's large angular scales, for RS it's smaller scales), there is a distortion in the CMB that does not correspond to effects that occur at recombination.

  • Patricia J Lampens added an answer:
    Can you identify?

    I am a science professor at the Lebanese university, and I have interests about astronomy physics... I have a telescope (150/1400 mm). I have observed something strange (a group of blue stars surrounded by a group of red stars),(photos attached). I believe that it is a globular cluster but I'm not sure, and I'm certain that isn't out of focus. Can you please recognize what i have observed and if it is discovered ?.

    + 2 more attachments

    Patricia J Lampens

    Hello, it seems to me that it is an instrumental pattern (maybe some faint stars superposed too). What type of camera did you use? To know for sure, you need to take a few calibration frames such as a bias, dark (subtraction) and flat-field (division). Only after taking out these effects, could you tell what you observed on the image. There is an additional edge effect too, which makes the halo appear asymmetric.  You could consult a manual from any software application useful for this, and find some basic information on the internet , e.g. even from a company which sells CCD camera's.

    For example, some definitions are given at

  • Charles Francis added an answer:
    Why are there different gases for different galaxies?
    In different galaxies there appear different gas structures. What is the mechanism adapting certain gases in certain galaxies while excluding the other gases?
    Charles Francis

    Of relevance may be that there is continuing star formation in spiral galaxies, but not in elliptical galaxies.

  • Mohamed Th. S. Heikal added an answer:
    Is it possible to find pure iron phase in meteorite without any inclusions?

    In the Chelyabinsk meteorite in particular.

    Mohamed Th. S. Heikal

    Iron meteorites were strongly used by ancient Egyptians as a tool in agriculture and other uses. I strongly  some colleagues about pure iron associated with Ni & Co as mentioned in Kamel impact crater crater of Egypt.

  • Manuel Morales added an answer:
    As a researcher claimed that black holes do not exist , is any one interested in finding non singular general relativity?

    A researcher claimed that black holes do not exist the link is:

    Is any one interested in solving the singularity problem in general relativity?

    What are the suggested ideas?

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      [Show abstract] [Hide abstract]
      ABSTRACT: A star collapsing gravitationally into a black hole emits a flux of radiation, knowns as Hawking radiation. When the initial state of a quantum field on the background of the star, is placed in the Unruh vacuum in the far past, then Hawking radiation corresponds to a flux of positive energy radiation travelling outwards to future infinity. The evaporation of the collapsing star can be equivalently described as a negative energy flux of radiation travelling radially inwards towards the center of the star. Here, we are interested in the evolution of the star during its collapse. Thus we include the backreaction of the negative energy Hawking flux in the interior geometry of the collapsing star and solve the full 4-dimensional Einstein and hydrodynamical equations numerically. We find that Hawking radiation emitted just before the star passes through its Schwarzschild radius slows down the collapse of the star and substantially reduces its mass thus the star bounces before reaching the horizon. The area radius starts increasing after the bounce. Beyond this point our program breaks down due to shell crossing. We find that the star stops collapsing at a finite radius larger than its horizon, turns around and its core explodes. This study provides a more realistic investigation of the backreaction of Hawking radiation on the collapsing star, that was first presented in [1].
      Preview · Article · Sep 2014
    Manuel Morales

    Although my invite for research contributions are initially focused towards grade school children, I invite my colleagues here at RG to feel free to participate as well (see link).

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      [Show abstract] [Hide abstract]
      ABSTRACT: Abstract: Grade school, high school, and college students as well as the general public are invited to verify if the scientific method needs an overhaul by simply doing searches for the keywords "direct selection" and "indirect selection" in peer-reviewed scientific papers. In doing so, the public will be able to confirm if experiments used to validate quantum mechanic theories are based on a fundamental omission error or not. The attached "Flawed Scientific Method" document was designed to go with the public invitation to help science self-correct. In essence, this one page document illustrates the mechanics of the discovery of Einstein's nonlocal hidden variables which in turn revealed how the scientific method is flawed and how to fix it.
      Full-text · Article · Sep 2015
  • Mohammad Ayaz Ahmad added an answer:
    What is the structure of black holes?
    In some books popularizing science (e.g. “Astronomy for dummies” by S.P. Maran) it is written that black holes have the following structure: falling matter, event horizon, singularity. This structure does not coincide with the classification used in special literature where the accretion disk forming by falling matter is included. Is the black hole structure in the book above an adequate explanation for non-specialists?
    Mohammad Ayaz Ahmad

    Really, we do not know what the inside of a black hole. Describing the characteristics of the structure of a black hole still remains one of the challenges of modern relativistic astrophysics.

  • V. G. Kurt added an answer:
    What are the popular plotting softwares that astromomers and astrophysicists use for publication? I am using XMGRACE and GNUPLOT? What about Matlab?

    Supermongo and IDL are also very popular among astrophysicists. Are Matlab, Mathematica, Xmgrace, Gnuplot also popular among some groups?

    V. G. Kurt

    I prefere MATLAB, but I know some my friends which like MATCAD. I suppose that all depend from personal experiance. For plot of results of calculation by MATLAD I preferre very simple program which made my friend Alex Berezin special for this purpose. Vladimir G. Kurt. 

  • Xiangqian Wu added an answer:
    How can I calculate or where can I find the selenographic coordinate of the point where the Sun is at zenith?

    I need to know the time-varying location, in terms of selenographic latitude and longitude, of the point where the line connecting the centers of the Sun and Moon intersects with the lunar surface, to the accuracy of second and kilometer, from 2000 to 2020. Thanks!

    Xiangqian Wu

    Thanks a lot!

  • Michael Peck added an answer:
    What is causing Dark Flow?

    Dark flow is an astrophysical term describing a possible non-random component of the peculiar velocity of galaxy clusters. The actual measured velocity is the sum of the velocity predicted by Hubble's Law plus a possible small and unexplained (or dark) velocity flowing in a common direction.

    Does Dark flow exits ? If yes what is the cause of it?

    Michael Peck

    1. There are many affects due to sample dependence, analytical methods and luminosity distance; I'm in no way saying you are unaware of them. However, I do think it is important to consider that the great attractor is estimated to be 80 Mpc away relative to the extent of the dark flow (at least 800 Mpc or almost 0.2z).

    2. I've only looked at articles by Kashlinsky and/or Atrio-Barandela, as there was controversy surrounding the Planck analysis by others.

    3. The question was asking about the source of the dark flow, which I suppose I can offer an answer to. Consider a sink-source universe with a cosmological scale gravitation potential, i.e. no energy is created or destroyed. The simplest solution would be a continuous, but collaminated 'big bang' arising from the center of the potential (CMB -> gravitational redshift). This than forms into the locally hot x-ray clusters, various galaxies and a Hubble flow, where the bulk flow begins to fall back into the potential (the "dark flow"). Gravitational lensing will then project local geodesics towards the center; i.e. we are observing objects accelerating back into a global gravitational potential through a cosmological-scale lens. This would further explain why volume element/angular scale observations support a static metric, increased entropy with redshift (cold baryonic matter, metallicity and mergers) and hemispherical anomalies versus homogenous universe.

  • Robert Loughnane added an answer:
    Is there a database of community-available antennas - beam size and efficiencies?

    Is it possible to source a URL or database of the available antennas in the field of millimeter and submillimeter astronomy?

    I need to be able to tabulate available frequency-dependent beamsizes and antenna efficiencies.

    Robert Loughnane

    True Johannes, but the beamsizes usually stated in the observing section of a specified article generally represent a frequency range. However, your point is noted. Thanks.

  • Fatemeh Tabatabaei added an answer:
    What methods are the best to measure the metallicity in the ISM?

    There are several methods and observers which can be used to estimate the metallicity in the interstellar medium, most of which are based on the measurements in the HII regions. First, what methods give the most reliable estimate? Second, has there been any measurement in more diffuse ISM in the Milky Way?

    Fatemeh Tabatabaei

    The radial gradient is an observational fact (which even could have been complicated by migration of stars in some cases). In any case, the environmental effects and the star formation feedback should not be neglected.

  • Ksh. Newton Singh added an answer:
    What will be the speed of sound in quark star if we consider EOS proposed by MIT bag model for an anisotropic fluid?

    If we consider MIT Bag Model EOS, the square of speed of sound for quark star should be around 0.33. But whether this is true for an anisotropic quark star or not. So whether EOS from MIT Bag Model is for isotropic or anisotropic matter or for both?

    Ksh. Newton Singh

    Thanks Prof. Uechi

  • Ksh. Newton Singh added an answer:
    Does a free fall collapsing dust radiate gravitational waves?

    A collapsing star when explode (supernova), due to the sudden ejection of massive mass around the central core, there is a disturbance in space-time leading to emission of gravitational waves. But what will happen if a collapsing goes on till black hole is formed, without any explosion? Will there be an emission of gravitational waves due to the continuous grow in curvature because of the growing mass?

    Ksh. Newton Singh

    Thank You Dr. Yang

  • Marshall Eubanks added an answer:
    How do I determine the spin rate of solivagant exoplanets and substellar objects?

    Solivagant (nomadic) planets are roaming the interstellar space. Depending on the steepness of the mass ditribution law, There may be significantly more substellar objects in the vicinity of the Sun than there are normal stars. A few nearby extremely cool object of super-Jupiter mass have been discovered (e.g., one with WISE). Despite the absence of light, such systems of planetary mass may be teeming with life. According to M. Eubanks, more solivagant planets will be observed in the future with JWST, ALMA and SPICA. My calculations show that the tidal heating of Earth generated by the Moon may presently come up to ~5 TW. A heat source of this order can sustain a massive subsurface ocean on a lonely exoearth for gigayears. The question is, how to observationally verify that nearby solivagant planets rapidly rotate? The spin rate of some stars has been determined photometrically from the modulations caused by persistent features (dark or hot spots) on the photospheres. Would that be the best way to observe the spin of very cold planets? Are there other possibilities?

    Marshall Eubanks

    Most galaxies, projected on the sky, are elliptical, and so there are a number of papers dealing with lens ellipticity (oblateness) for strong lensing (see below). I  do not think there will be much difficulty in introducing this into the microlensing formalism. Whether or not the data will be good enough to actually determine nomad rotation oblateness is, of course, another question.

  • Markiyan Semenovich Chubey added an answer:
    Is there a future for ground-based astrometry after GAIA?
    Considering the revolution that occurred in terms of optical astrometry due to astrometric satellites such as Hipparcos (even though there were parallel developments and major improvements on ground-based astrometric telescopes), an even larger jump is about to occur with the GAIA astrometric mission. Much work will need to be done to tie the radio reference frame (ICRF2) to the GAIA optical reference frame. There will be ground-based follow-up work following GAIA detections, proper motions and parallax work, as satellite missions are relatively short lived and expensive. But, what does the future hold for ground-based astrometry? Near Earth objects? Solar system measurements? Reference frame maintenance?
    Markiyan Semenovich Chubey

    Greetings to all.

    The microarcsecond astrometry after Gaia in reality rather will be on the level of 0.05 milliarccecond because of the correlation between the parameters of the movement of technical systems (space craft vibrations, orbital and rotational movement, parameters of the instrument and its registration system, timing and pure astrographyc fits and probably some others sources, that I cannot foreseen). We must accept the opinion of David Dunham about observations of the Solar system bodies. Including, surely, the ground-based astrometric observations.

    The real problem does exist in the fitting (rather recreation) of the Celestial coordinate frame, the movements of the celestial bodies in which the real theories of baricentric  movements are traditionally been constructing on the base of the laws of the mechanical energy conservation. There are plenty of the work in that area for which the ground-based astrometry will be required. 

    It is reasonable to wait the appearance of the other space projects for detalization of the hardly solving question in Gaia project and independent other questions. For instance, involving or prolongation of the Gaia's results into diapason of the more faint stars. See, for instance, Baltic Astronomy, 24, 84–91, 2015.   

  • Marcelo Negri Soares added an answer:
    What is antigravity?
    I want to know the basics.
    Marcelo Negri Soares

    Anti-gravity is an idea of creating a place or object that is free from the force of gravity. It does not refer to the lack of weight under gravity experienced in free fall or orbit, or to balancing the force of gravity with some other force, such as electromagnetism or aerodynamic lift. Anti-gravity is a recurring concept in science fiction, particularly in the context of spacecraft propulsion. An early example is the gravity blocking substance "Cavorite" in H. G. Wells' The First Men in the Moon.

    In Newton's law of universal gravitation, gravity was an external force transmitted by unknown means. In the 20th century, Newton's model was replaced by general relativity where gravity is not a force but the result of the geometry of spacetime. Under general relativity, anti-gravity is impossible except under contrived circumstances. Quantum physicists have postulated the existence of gravitons, a set of massless elementary particles that transmit the force, and the possibility of creating or destroying these is unclear.

    "Anti-gravity" is often used colloquially to refer to devices that look as if they reverse gravity even though they operate through other means, such as lifters, which fly in the air by using electromagnetic fields.

  • Alexander Chepick added an answer:
    How can we explain Tifft's quantization of galaxy redshift?
    The reports by Tifft on quantization of galactic redshift are well-known to astronomers. Read for example See also a recent review on redshift theories by Marmet at
    Alexander Chepick

    I don't have articles on Tifft's quantization, but I will send you two of my articles on static models.
    I think that the space of the Universe is not expanding. Test Tifft's quantization will show it, because in the framework of GR the distance between galaxies previously had to be less than it is now. Therefore, in GR dependence should be approximately inversely proportional to z.

  • John Houghton added an answer:
    Proton- proton reaction in star center can anyone help?
    The proton-proton reaction in star center goes on for billions of years. But when the reaction starts on the surface as in the case of the nova, it only lasts for a few weeks. Can somebody explain this difference?
  • William Dean Pesnell added an answer:
    How can we analytically calculate the Hurst exponent for a periodic function?

    Let's focus on a sin(x) function. I tried using the DMA (changing sums into integrals) and the series width w(l) from Katsev & L'Hereux, Computers & Geosciences 29 (2003) 1085–1089. In the first case I got stuck with some crazy functions, and in the second (expanding logs in time series to first order as l<<T) I got... H= -1/2. I want to precisely understand why H=1 for strict periodicity.

    William Dean Pesnell

    An R/S analysis compares the properties of the time series over many different time scales. The slope of the curve then approximates the Hurst exponent. If you analyze a series with noise and a sine curve you see a discontinuity in the slope at the period of the sine curve (the Suyal et al. 2009 paper has some examples). In the absence of variations at longer timescales, such as trends, there is no information above that period to derive a slope. For the sunspot number we see a discontinuity at 11 years, just as expected, but there are longer-term signals to continue the R/S analysis at longer periods. That gives an estimate of H for the entire time series. A linear trend indeed has H=1 because the variation over a time bin is comparable to or larger than the noise within that time bin.

  • Z. Osmanov added an answer:
    Does anyone know what is the minimum level for detectability of PeV photons by modern telescopes?

    One of the important questions concerning this topic is to know sensitivity of instruments - the minimum detectable flux.

    Z. Osmanov

    Dear Dr Samvel Ter-Antonyan, thank you for the useful references


  • Gerro Prinsloo added an answer:
    How can we compute solar position at a given place on a given day and time?
    I have GPS obtained UTC time (hours, minutes, seconds), longitude(deg E), latitude (deg N) and date. I have thoroughly search on internet for step-by-step procedure to obtain solar position variables - solar zenith angle, solar azimuth angle, Sun-Earth distance. But every method is different. Some followed geometrical method while most others have some complicated formulae with varying coefficients. I never found a generalized way to obtain solar position variables. Is there any reference which provides step-by-step procedure to obtain them in the most accurate way? Can anyone provide the step-by-step procedure with equations, corresponding explanation for coefficients, accuracy of output and literature references for each equation? Please don't provide me readily available codes / functions or links on internet search.
    Gerro Prinsloo

    Dear Lakshmi

    you already have many responses, but if you require open source algorithms for sun tracking with matlab simulink or PLC or microprocessors then you can also check Chapter 3 of our free eBook for links to the code:



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      [Show abstract] [Hide abstract]
      ABSTRACT: This free book details Solar-Tracking, Automatic Sun-Tracking-Systems and Solar-Trackers and Solar Energy Harvesting Mechanisms. Book and literature review is ideal for building sun tracker, sun tracker control automation, sun and moon tracking and sunshine tracking in solar applications for sun-rich countries such as the USA, Spain, Portugal, Mediterranean, Italy, Greece, Mexico, Portugal, China, India, Brazil, Chili, Argentina, South America, UAE, Saudi Arabia, Middle East, Iran, Iraq, etc. A solar harvester and tracker is a device that orients a payload toward the sun. A programmable computer based solar tracking device includes principles of solar tracking, solar tracking systems, as well as microcontroller, microprocessor and/or PC based solar tracking control to orientate solar reflectors, solar lenses, photovoltaic panels or other optical configurations towards the sun (see solar parabola calculator designer Motorized space frames and kinematic systems ensure motion dynamics and employ drive technology and gearing principles to steer optical configurations such as mangin, parabolic, conic, or cassegrain solar energy collectors to face the sun and follow the sun movement contour continuously (Download Center). The content of the book is also applicable to communication antenna satellite tracking and moon tracking algorithm source code for which links to free download links are provided, including formulas and algorithms to calculate the daily ephemeris of the sun position (and moon position ephimeris) for the years 1900 to 2035 AD and beyond. Sun tracking suitable for renewable energy systems RES concentrated solar CSP Stirling micro-CHP micro-CCHP co-generation combined cycle micro combined heat and power micro-CHCP in tri-generation, quad-generation and poly-generation with smart-microgrid and smartgrid applications in remote power systems and isolated microgrid for decentralized energy power systems.. In harnessing power from the sun through a solar tracker or practical solar tracking system, renewable energy control automation systems require automatic solar tracking software and solar position algorithms to accomplish dynamic motion control with control automation architecture, circuit boards and hardware. On-axis sun tracking system such as the altitude-azimuth dual axis or multi-axis solar tracker systems use a sun tracking algorithm or ray tracing sensors or software to ensure the sun's passage through the sky is traced with high precision in automated solar tracker applications, right through summer solstice, solar equinox and winter solstice (seguimiento solar y automatización, automatización seguidor solar, tracking solar e automação, automação seguidor solar, inseguimento solare, inseguitore solare, energia termica, sole seguito, posizionatore motorizzato) . From sun tracing software perspective, the sonnet Tracing The Sun has a literal meaning. Within the context of sun track and trace, this book explains that the sun's daily path across the sky is directed by relatively simple principles, and if grasped/understood, then it is relatively easy to trace the sun with sun following software. Sun position computer software and the physics behind tracing the sun are available as open source code, sources that is listed in this book. Ironically there was even a system called sun chaser, said to have been a solar positioner system known for chasing the sun throughout the day. Using solar equations in an electronic circuit for solar tracking is quite simple, even if you are a novice, but mathematical solar equations are over complicated by academic experts and professors in text-books, journal articles and internet websites. In terms of solar hobbies, scholars, students and Hobbyist's looking at solar tracking electronics or PC programs for solar tracking are usually overcome by the sheer volume of scientific material and internet resources, which leaves many developers in frustration when search for simple experimental solar tracking source-code for their on-axis sun-tracking systems. This booklet will simplify the search for the mystical sun tracking formulas for your sun tracker innovation and help you develop your own autonomous solar tracking controller. Even the Scheffler reflector design or calculations of a Scheffler fixed focus concentrator. Sheffler reflector construction in a manual sun tracking system for a Scheffler concentrator needs some analysis. By directing the solar collector directly into the sun, a solar harvesting means or device can harness sunlight or thermal heat. This is achieved with the help of sun angle formulas, solar angle formulas or solar tracking procedures for the calculation of sun's position in the sky. Automatic sun tracking system software includes algorithms for solar altitude azimuth angle calculations required in following the sun across the sky. In using the longitude, latitude GPS coordinates of the solar tracker location, these sun tracking software tools supports precision solar tracking by determining the solar altitude-azimuth coordinates for the sun trajectory in altitude-azimuth tracking at the tracker location, using certain sun angle formulas in sun vector calculations. Instead of follow the sun software, a sun tracking sensor such as a sun sensor or webcam or video camera with vision based sun following image processing software can also be used to determine the position of the sun optically. Such optical feedback devices are often used in solar panel tracking systems and dish tracking systems. Dynamic sun tracing is also used in solar surveying, DNI analyser and sun surveying systems that build solar infographics maps with solar radiance, irradiance and DNI models for GIS (geographical information system). In this way geospatial methods on solar/environment interaction makes use use of geospatial technologies (GIS, Remote Sensing, and Cartography). Climatic data and weather station or weather center data, as well as queries from sky servers and solar resource database systems (i.e. on DB2, Sybase, Oracle, SQL, MySQL) may also be associated with solar GIS maps. In such solar resource modelling systems, a pyranometer or solarimeter is normally used in addition to measure direct and indirect, scattered, dispersed, reflective radiation for a particular geographical location. Sunlight analysis is important in flash photography where photographic lighting are important for photographers. GIS systems are used by architects who add sun shadow applets to study architectural shading or sun shadow analysis, solar flux calculations, optical modelling or to perform weather modelling. Such systems often employ a computer operated telescope type mechanism with ray tracing program software as a solar navigator or sun tracer that determines the solar position and intensity. The purpose of this booklet is to assist developers to track and trace suitable source-code and solar tracking algorithms for their application, whether a hobbyist, scientist, technician or engineer. Many open-source sun following and tracking algorithms and source-code for solar tracking programs and modules are freely available to download on the internet today. Certain proprietary solar tracker kits and solar tracking controllers include a software development kit SDK for its application programming interface API attributes (Pebble). Widget libraries, widget toolkits, GUI toolkit and UX libraries with graphical control elements are also available to construct the graphical user interface (GUI) for your solar tracking or solar power monitoring program. The solar library used by solar position calculators, solar simulation software and solar contour calculators include machine program code for the solar hardware controller which are software programmed into Micro-controllers, Programmable Logic Controllers PLC, programmable gate arrays, Arduino processor or PIC processor. PC based solar tracking is also high in demand using C++, Visual Basic VB, as well as MS Windows, Linux and Apple Mac based operating systems for sun path tables on Matlab, Excel. Some books and internet webpages use other terms, such as: sun angle calculator, sun position calculator or solar angle calculator. As said, such software code calculate the solar azimuth angle, solar altitude angle, solar elevation angle or the solar Zenith angle (Zenith solar angle is simply referenced from vertical plane, the mirror of the elevation angle measured from the horizontal or ground plane level). Similar software code is also used in solar calculator apps or the solar power calculator apps for IOS and Android smartphone devices. Most of these smartphone solar mobile apps show the sun path and sun-angles for any location and date over a 24 hour period. Some smartphones include augmented reality features in which you can physically see and look at the solar path through your cell phone camera or mobile phone camera at your phone's specific GPS location. In the computer programming and digital signal processing (DSP) environment, (free/open source) program code are available for VB, .Net, Delphi, Python, C#, C+, C++, Swift, ADM, F#, Flash, Basic, QBasic, GBasic, KBasic, SIMPL language, Squirrel, Solaris, Assembly language on operating systems such as MS Windows, Apple Mac, DOS or Linux OS. Software algorithms predicting position of the sun in the sky are commonly available as graphical programming platforms such as Matlab (Mathworks), Simulink models, Java applets, TRNSYS simulations, Scada system apps, Labview module, Beckhoff TwinCAT (Visual Studio), Siemens SPA, mobile and iphone apps, Android or iOS tablet apps, and so forth. At the same time, PLC software code for a range of sun tracking automation technology can follow the profile of sun in sky for Siemens, HP, Panasonic, ABB, Allan Bradley, OMRON, SEW, Festo, Beckhoff, Rockwell, Schneider, Endress Hauser, Fudji electric. Honeywell, Fuchs, Yokonawa, or Muthibishi platforms. Sun path projection software are also available for a range of modular IPC embedded PC motherboards, Industrial PC, PLC (Programmable Logic Controller) and PAC (Programmable Automation Controller) such as the Siemens S7-1200 or Siemens Logo, Beckhoff IPC or CX series, OMRON PLC, Ercam PLC, AC500plc ABB, National Instruments NI PXI or NI cRIO, PIC processor, Intel 8051/8085, IBM (Cell, Power, Brain or Truenorth series), FPGA (Xilinx Altera Nios), Xeon, Atmel megaAVR, or Arduino AtMega microcontroller, with servo motor, stepper motor, direct current DC pulse width modulation PWM (current driver) or alternating current AC SPS or IPC variable frequency drives VFD motor drives (also termed adjustable-frequency drive, variable-speed drive, AC drive, micro drive or inverter drive) for electrical, mechatronic, pneumatic, or hydraulic solar tracking actuators. The above motion control and robot control systems include analogue or digital interfacing ports on the processors to allow for tracker angle orientation feedback control through one or a combination of angle sensor or angle encoder, shaft encoder, precision encoder, optical encoder, magnetic encoder, direction encoder, rotational encoder, chip encoder, tilt sensor, inclination sensor, or pitch sensor. Note that the tracker's elevation or zenith axis angle may measured using an altitude angle-, declination angle-, inclination angle-, pitch angle-, or vertical angle-, zenith angle- sensor or inclinometer. Similarly the tracker's azimuth axis angle be measured with a azimuth angle-, horizontal angle-, or roll angle- sensor. Chip integrated accelerometer magnetometer gyroscope type angle sensors can also be used to calculate displacement. Other options include the use of thermal imaging systems such as a Fluke thermal imager, or robotic or vision based solar tracker systems that employ face tracking, head tracking, hand tracking, eye tracking and car tracking principles in solar tracking. With unattended decentralised rural, island, isolated, or autonomous off-grid power installations, remote control, monitoring, data acquisition, digital datalogging and online measurement and verification equipment becomes crucial. It assists the operator with supervisory control to monitor the efficiency of remote renewable energy resources and systems and provide valuable web-based feedback in terms of CO2 and clean development mechanism (CDM) reporting. A power quality analyser for diagnostics through internet, WiFi and cellular mobile links is most valuable in frontline troubleshooting and predictive maintenance, where quick diagnostic analysis is required to detect and prevent power quality issues. Solar tracker applications cover a wide spectrum of solar energy and concentrated solar devices, including solar power generation, solar desalination, solar water purification, solar steam generation, solar electricity generation, solar industrial process heat, solar thermal heat storage, solar food dryers, solar water pumping, hydrogen production from methane or producing hydrogen and oxygen from water (HHO) through electrolysis. Many patented or non-patented solar apparatus include tracking in solar apparatus for solar electric generator, solar desalinator, solar steam engine, solar ice maker, solar water purifier, solar cooling, solar refrigeration, USB solar charger, solar phone charging, portable solar charging tracker, solar coffee brewing, solar cooking or solar dying means. Your project may be the next breakthrough or patent, but your invention is held back by frustration in search for the sun tracker you require for your solar powered appliance, solar generator, solar tracker robot, solar freezer, solar cooker, solar drier, solar pump, solar freezer, or solar dryer project. Whether your solar electronic circuit diagram include a simplified solar controller design in a solar electricity project, solar power kit, solar hobby kit, solar steam generator, solar hot water system, solar ice maker, solar desalinator, hobbyist solar panels, hobby robot, or if you are developing professional or hobby electronics for a solar utility or micro scale solar powerplant for your own solar farm or solar farming, this publication may help accelerate the development of your solar tracking innovation. Lately, solar polygeneration, solar trigeneration (solar triple generation), and solar quad generation (adding delivery of steam, liquid/gaseous fuel, or capture food-grade CO2) systems have need for automatic solar tracking. These systems are known for significant efficiency increases in energy yield as a result of the integration and re-use of waste or residual heat and are suitable for compact packaged micro solar powerplants that could be manufactured and transported in kit-form and operate on a plug-and play basis. Typical hybrid solar power systems include compact or packaged solar micro combined heat and power (CHP or mCHP) or solar micro combined, cooling, heating and power (CCHP, CHPC, mCCHP, or mCHPC) systems used in distributed power generation. These systems are often combined in concentrated solar CSP and CPV smart microgrid configurations for off-grid rural, island or isolated microgrid, minigrid and distributed power renewable energy systems. Solar tracking algorithms are also used in modelling of trigeneration systems using TrnSys, Matlab and Simulink platforms as well as in automation and control of renewable energy systems through intelligent parsing, multi-objective, adaptive learning control and control optimization strategies. Solar tracking algorithms also find application in developing solar models for country or location specific solar studies, for example in terms of measuring or analysis of the fluctuations of the solar radiation (i.e. direct and diffuse radiation) in a particular area. Solar DNI, solar irradiance and atmospheric information and models can thus be integrated into a solar map, solar atlas or geographical information systems (GIS). Such models allows for defining local parameters for specific regions that may be valuable in terms of the evaluation of different solar in photovoltaic of CSP systems on simulation and synthesis platforms such as Matlab and Simulink or in linear or multi-objective optimization algorithm platforms such as COMPOSE, EnergyPLAN or DER-CAM. A dual-axis solar tracker and single-axis solar tracker may use a sun tracker program or sun tracker algorithm to position a solar dish, solar panel array, heliostat array, PV panel, solar antenna or infrared solar nantenna. A self-tracking solar concentrator performs automatic solar tracking by computing the solar vector. Solar position algorithms (TwinCAT, SPA, or PSA Algorithms) use an astronomical algorithm to calculate the position of the sun. It uses astronomical software algorithms and equations for solar tracking in the calculation of sun's position in the sky for each location on the earth at any time of day. Like an optical solar telescope, the solar position algorithm pin-points the solar reflector at the sun and locks onto the sun's position to track the sun across the sky as the sun progresses throughout the day. Optical sensors such as photodiodes, light-dependant-resistors (LDR) or photoresistors are used as optical accuracy feedback devices. Lately we also included a section in the book (with links to microprocessor code) on how the PixArt Wii infrared camera in the Wii remote or Wiimote may be used in infrared solar tracking applications. In order to harvest free energy from the sun, some automatic solar positioning systems use an optical means to direct the solar tracking device. These solar tracking strategies use optical tracking techniques, such as a sun sensor means, to direct sun rays onto a silicon or CMOS substrate to determine the X and Y coordinates of the sun's position. In a solar mems sun-sensor device, incident sunlight enters the sun sensor through a small pin-hole in a mask plate where light is exposed to a silicon substrate. In a web-camera or camera image processing sun tracking and sun following means, object tracking software performs multi object tracking or moving object tracking methods. In an solar object tracking technique, image processing software performs mathematical processing to box the outline of the apparent solar disc or sun blob within the captured image frame, while sun-localization is performed with an edge detection algorithm to determine the solar vector coordinates. An automated positioning system help maximize the yields of solar power plants through solar tracking control to harness sun's energy. In such renewable energy systems, the solar panel positioning system uses a sun tracking techniques and a solar angle calculator in positioning PV panels in photovoltaic systems and concentrated photovoltaic CPV systems. Automatic on-axis solar tracking in a PV solar tracking system can be dual-axis sun tracking or single-axis sun solar tracking. It is known that a motorized positioning system in a photovoltaic panel tracker increase energy yield and ensures increased power output, even in a single axis solar tracking configuration. Other applications such as robotic solar tracker or robotic solar tracking system uses robotica with artificial intelligence in the control optimization of energy yield in solar harvesting through a robotic tracking system. Automatic positioning systems in solar tracking designs are also used in other free energy generators, such as concentrated solar thermal power CSP, dish Stirling systems and concentrated solar power systems for absorption chillers. The sun tracking device in a solar collector in a solar concentrator or solar collector Such a performs on-axis solar tracking, a dual axis solar tracker assists to harness energy from the sun through an optical solar collector, which can be a parabolic mirror, parabolic reflector, Fresnel lens or mirror array/matrix. A parabolic dish or reflector is dynamically steered using a transmission system or solar tracking slew drive mean. In steering the dish to face the sun, the power dish actuator and actuation means in a parabolic dish system optically focusses the sun's energy on the focal point of a parabolic dish or solar concentrating means. A Stirling engine, solar heat pipe, thermosyphin, solar phase change material PCM receiver, or a fibre optic sunlight receiver means is located at the focal point of the solar concentrator. The dish Stirling engine configuration is referred to as a dish Stirling system or Stirling power generation system. Hybrid solar power systems (used in combination with biogas, biofuel, petrol, ethanol, diesel, natural gas or PNG) use a combination of power sources to harness and store solar energy in a storage medium. Any multitude of energy sources can be combined through the use of controllers and the energy stored in batteries, phase change material, thermal heat storage, and in cogeneration form converted to the required power using thermodynamic cycles (organic Rankin, Brayton cycle, micro turbine, Stiling) with an inverter and charge controller. Using exergy analysis principles, several exergetic variables are used to identify the strength and limitations of a system. Book is ideal for solar applications in sun rich countries such as Spain, Mediterranean, Italy, Greece, Mexico, Portugal, China, India, Brazil, Chili, Argentina, etc. В этой книге подробно Автоматическая Solar-Tracking, ВС-Tracking-Systems, Solar-трекеры и ВС Tracker Systems. Интеллектуальный автоматический солнечной слежения является устройством, которое ориентирует полезную нагрузку к солнцу. Такое программируемый компьютер на основе солнечной устройство слежения включает принципы солнечной слежения, солнечных систем слежения, а также микроконтроллер, микропроцессор и / или ПК на базе управления солнечной отслеживания ориентироваться солнечных отражателей, солнечные линзы, фотоэлектрические панели или другие оптические конфигурации к ВС Моторизованные космические кадры и кинематические системы обеспечения динамики движения и использовать приводной техники и готовится принципы, чтобы направить оптические конфигурации, такие как Манжен, параболических, конических или Кассегрена солнечных коллекторов энергии, чтобы лицом к солнцу и следовать за солнцем контур движения непрерывно. В обуздывать силу от солнца через солнечный трекер или практической солнечной системы слежения, системы возобновляемых контроля энергии автоматизации требуют автоматического солнечной отслеживания программного обеспечения и алгоритмов солнечные позиции для достижения динамического контроля движения с архитектуры автоматизации управления, печатных плат и аппаратных средств. На оси системы слежения ВС, таких как высота-азимут двойной оси или многоосевые солнечные системы трекер использовать алгоритм отслеживания солнце или трассировки лучей датчиков или программное обеспечение, чтобы обеспечить прохождение солнца по небу прослеживается с высокой точностью в автоматизированных приложений Солнечная Tracker , прямо через летнего солнцестояния, солнечного равноденствия и зимнего солнцестояния.Высокая точность позиции ВС калькулятор или положение солнца алгоритм это важный шаг в проектировании и строительстве автоматической системой солнечной слежения. 这本书详细介绍了全自动太阳能跟踪,太阳跟踪系统的出现,太阳能跟踪器和太阳跟踪系统。智能全自动太阳能跟踪器是定向向着太阳的有效载荷设备。这种可编程计算机的太阳能跟踪装置,包括太阳跟踪,太阳能跟踪系统,以及微控制器,微处理器和/或基于PC机的太阳跟踪控制,以定向太阳能反射器,太阳透镜,光电板或其他光学配置朝向太阳的原理。机动空间框架和运动系统,确保运动动力学和采用的驱动技术和传动原理引导光学配置,如曼金,抛物线,圆锥曲线,或卡塞格林式太阳能集热器面向太阳,不断跟随太阳运动的轮廓。 从阳光透过太阳能跟踪器或实用的太阳能跟踪系统利用电力,可再生能源控制的自动化系统需要自动太阳跟踪软件和太阳位置算法来实现控制与自动化架构,电路板和硬件的动态运动控制。上轴太阳跟踪系统,如高度,方位角双轴或多轴太阳跟踪系统使用太阳跟踪算法或光线追踪传感器或软件,以确保通过天空中太阳的通道被跟踪的高精度的自动太阳跟踪器的应用,通过正确的夏至,春分太阳和冬至。一种高精度太阳位置计算器或太阳位置算法是这样的自动太阳能跟踪系统的设计和施工中的重要一步。 This Solar Tracking Practical Research eBook for Apple iPad, Barnes and Noble Nook, Sony Reader, BeBook, Adobe Digital Editions, Lexcycle Stanza, BookGlutton, AZARDI, Aldiko, WordPlayer on Android Mozilla Firefox add-on OpenBerg Lector can be down be downloaded on the link:
      Full-text · Book · Aug 2014
  • D D Pawar added an answer:
    What is the use of dark energy in f(r,t) theory?

    Can we get any help of dark energy momentum tensor in f(r,t) theory?

    D D Pawar

    Thank  You So much...for the valuable answers!!

  • Vikram Zaveri added an answer:
    Can we use Kepler's third law to calculate orbital period of a star in a galaxy?

    Kepler's third law yields correct orbital periods for the planets of the solar system
    however, orbital period of the Sun in the Milky Way is computed with the relation    P = 2*pi*r/v.  Analysis given in the article "Supplement to periodic relativity" shows that we can obtain same result by introducing proper time in the form of deviation factor into Kepler's third law. This deviation to flat Minkowski metric satisfies Einstein's field equations and also provides solution to rotation curves of galaxies.

    • Source
      [Show abstract] [Hide abstract]
      ABSTRACT: Additional explanation relating to derivation of deflection of light is presented. Curvilinear acceleration is distinguished from the Newtonian polar conic acceleration. The diference between the two is due to the curvature term. Lorentz invariant expression for acceleration is derived. Theory of rotation curves of galaxies based on second solution to Einstein's field equation is presented. Unification of periodic relativity and quantum mechanics results in periodic quantum gravity and cosmology theory.
      Full-text · Article · Aug 2014
    Vikram Zaveri

    Following article is now published in "Progress in Physics"
    Zaveri V.H., Periodic relativity: deflection of light, acceleration, rotation curves. Progress in Physics, 2015, v.11(1), 43-49.

  • Hassan Sedaghat added an answer:
    Do dark matter and dark energy constitute valid evidence of large spatial dimensions higher than 3?
    There are speculations that the gravitational effects of matter in 4 or greater LARGE spatial dimensions might account for the substantial discrepancy that exists between measured gravitational effects on normal baryonic matter and the amount of that matter that exists according to measurements. Could we be measuring the gravitational effects of "normal" matter in higher dimensions? And can large higher dimensions also explain the huge amount of dark energy that seems to be around?
    Hassan Sedaghat

    Thomas, thank you for sending the second chapter of your book. The correlations idea adds another angle from which to look at this issue. 

  • Richard Gauthier added an answer:
    Why are mainstream physicists against the super luminal physics?

    Why are mainstream physicist generally against theories, which describe faster than speed motion or communication? Is it proven in experimentally that it cannot happen or is it just a bias based on reputation of the existing theories? There are 2 very good papers about faster than light relativity listed at the bottom. Has someone refuted them on specifics?

    The papers are: .

    + 1 more attachment

    Richard Gauthier

    Hello Nainan,

    It is clear that you are a materialist and that you think that you know what matter is--the fundamental substance of the material world, and the material world is the only real world for you. You are welcome to your circular opinion, but please do not think that it is logical, or scientific. There is no scientific reason to think that the substance of matter is matter. Substance is that on which matter stands, and that substance does not have to be material-- it may be energy, it may be consciousness, it may be something non-material. Matter is a concept used to help unify our sense impressions, which are surely mental and not material. And concepts are mental also.

    with best wishes,


  • Fabio Salvaggio added an answer:
    What kind of camera do I need to do transit photometry?

    I am working with a small group of students at Hamline University on observing an exoplanet using transit photometry.

    Right now, our group is working on buying equipment. The school already has Celestron C-8 telescopes with motorized mounts available for us to use, but we don't have a camera. We need a camera that we can use to take a long-exposure photograph of a single star, and it needs to be able to measure the brightness of the star very accurately.

    Our budget is about $1,000, but the cheaper the better. So far, the only camera under $1,000 I have found that might work is the Atik Titan.  One person I asked about this camera said that the anti-blooming technology might cause problems, and that the chip in the Atik Titan is too small.  This person proposed the ST-402ME as a better model, but it costs $1,500.

    Does anyone know either of these cameras would be sufficient for our project?  Is it worth the extra money to buy the ST-402? Or do you have any other recommendations?

    Many thanks in advance for any help!

    + 2 more attachments

    Fabio Salvaggio

    I always used SBIG ST cameras. ST7 and ST8. I'm pretty sure you can find them as used with a good price (ST7 for sure). With these cameras I achieved great precision (better than 0.002) with a C9.25 at f/10. You can see in my blog ( translate it and go in exoplanet category) and in some paper I published.

  • Patrice Poyet added an answer:
    Telescope for amateur astronomy.
    I am a researcher at a science education project in Palestine and I coordinate for an informal science program. Many of the students I work with are interested in astronomy and space. I would like to purchase a telescope for amateur astronomy so as to maintain their interest and have astronomy-related activities at our center. I have been researching for the best amateur astronomy telescope and I have asked for advice, but I would like to hear your thoughts as experts in astronomy. One of the telescopes I am currently looking at is Celestron's CGEM - 1100 Computerized Telescope, what are your thoughts on this one? I truly appreciate any feedback / advice you may provide.
    Patrice Poyet

    I would strongly recommend to make it as it will teach your young students a lot of things and make them share a great adventure. The book from Texereau is perfect for that

    Would you like to have a look at the telescopes I built myself got to:



  • Dmitri Martila added an answer:
    Which experiment can determine if our universe is hologram or not?

    Which experiment can determine if our universe is hologram or not?

    Is it confirmed yet or still is it an open question?


    Bhushan Poojary.

    Dmitri Martila

    @Indranil Banik

    Perhaps you find it amusing: "Entropy of Real Pendulum"

  • David Iain Pontin added an answer:
    What are the fan and spine reconnections in the 3D magnetic reconnection of the solar corona?

    How do the fan and spine reconnections take place?

    David Iain Pontin

    This terminology refers to magnetic reconnection in the vicinity of a three-dimensional magnetic null point (a point in space at which the magnetic field strength is zero). Electric current sheets can form in various configurations around these points in response to different external forces, leading to different types of reconnection. A summary of the properties of these types of reconnection, as well as references to various articles with further details, can be found in the attached review.

    • Source
      [Show abstract] [Hide abstract]
      ABSTRACT: The magnetic field in many astrophysical plasmas -- such as the Solar corona and Earth's magnetosphere -- has been shown to have a highly complex, three-dimensional structure. Recent advances in theory and computational simulations have shown that reconnection in these fields also has a three-dimensional nature, in contrast to the widely used two-dimensional (or 2.5-dimensional) models. Here we discuss the underlying theory of three-dimensional magnetic reconnection. We also review a selection of new models that illustrate the current state of the art, as well as highlighting the complexity of energy release processes mediated by reconnection in complicated three-dimensional magnetic fields.
      Full-text · Article · Jan 2011 · Advances in Space Research

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